Presumably if he had then moved the keys, he's just committed a crime again, so we're back in business. If he'd sat on the keys forever, he would never be prosecuted.
Impossible to know. Unless the feds deny there is an investigation, it's always possible that an investigation is ongoing. It's possible to extend the statute of limitations with sealed indictment under what is called a John Doe defendant. This loophole was employed in the DB Cooper case.